JP2005314593A - Biaxially stretched polytetrafluoroethylene porous film and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a biaxially stretched polytetrafluoroethylene porous film substantially dissolving anisotropy in suture tearing strength and tensile strength without damaging flexibility, improving their strengths themselves and also capable of freely designing porosity rate and hole diameter. <P>SOLUTION: This biaxially stretched polytetrafluoroethylene porous film has ≥300 g suture tearing stress in any of lengthwise and transverse directions and ≤20% difference in suture tearing strengths of lengthwise and transverse directions. The method for producing the porous film comprises a process of compressing the biaxially stretched film between its stretching process and sintering process. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention is biaxially stretched so that mechanical anisotropy is substantially eliminated and porosity can be freely designed without impairing the inherent flexibility of the biaxially stretched polytetrafluoroethylene porous membrane. The present invention relates to a polytetrafluoroethylene porous membrane and a method for producing the same.

  An expanded polytetrafluoroethylene porous body produced by stretching polytetrafluoroethylene (hereinafter abbreviated as “PTFE”) is composed of a large number of fine fibrils (microfibers) and a large number of nodes (nodules) connected to each other by the fibrils. ), And this microstructure forms a continuous porous structure. In the expanded PTFE porous body, a porous structure such as a pore diameter and a porosity can be arbitrarily set by controlling stretching conditions.

  The expanded PTFE porous body has a porous structure in addition to the characteristics such as heat resistance and chemical resistance of PTFE itself and surface characteristics such as low coefficient of friction, water repellency, and non-adhesiveness. In addition, properties such as fluid permeability, particulate collection, filterability, low dielectric constant, and low dielectric loss tangent are added. PTFE itself is a hard and brittle resin, but the expanded PTFE porous body has a good flexibility because it has a porous structure.

  Since the expanded PTFE porous material has such unique excellent properties, its use in the general industrial field and the medical field is expanding. The expanded PTFE porous material is widely used as, for example, a cushion material, a seal material, and a spacer. In clothing applications, the expanded PTFE porous body has moisture permeability, water resistance, heat retention, etc., and is used, for example, in the manufacture of various clothing items such as trekking wear, rain wear, ski wear, shoes, and gloves. .

  In the medical field, expanded PTFE porous material has characteristics such as chemical stability, non-toxicity to the living body, non-degradability, and antithrombotic properties, so it is the most suitable material for applications that directly touch tissues in the body. It is. Moreover, since the expanded PTFE porous body can be flexibly changed in accordance with various in vivo tissue shapes, a patch material or an artificial blood vessel can be used as a porous body having a sheet-like or tubular structure. It is used as a medical polymer material such as a catheter and artificial cartilage substitute material.

  Expanded PTFE porous body with high porosity and large pore diameter, when used as an in vivo implant material such as artificial blood vessels, the surrounding tissue penetrates into the porous structure and forms a good healing state. Can do. On the other hand, in patch materials used for repairing the pericardium, pleura, diaphragm, peritoneum, tendon sheath, etc., it is necessary to avoid invasion and adhesion of surrounding tissues. An expanded PTFE porous body having a small pore size is suitable as a transplant material that requires such tissue blocking properties.

  The expanded PTFE porous body is generally manufactured in the form of a tube, a sheet (including a film), a monofilament, etc. Among them, the sheet-like expanded PTFE porous film is a cushion material, a sealing material, and a clothing. Widely used in applications such as medical materials and medical materials. The expanded porous PTFE membrane is not limited to a sheet shape formed from the beginning, but may be formed by cutting a tube into a sheet shape. Moreover, a tube and various structures can also be formed using an expanded PTFE porous membrane. For example, a tube can be formed by winding an expanded PTFE porous membrane around the outer peripheral surface of a rod-shaped support and heat-bonding the end portions or the overlapping portion or adhering them with an adhesive.

  However, the expanded PTFE porous membrane is generally characterized by strong mechanical anisotropy. Generally, an expanded PTFE porous membrane is formed by extruding a mixture of unsintered PTFE powder and a lubricant to produce a sheet-like or rod-like extrudate, and rolling the extrudate to obtain a rolled sheet. Produced by a rolling process for producing a non-sintered expanded PTFE porous film by stretching a rolled sheet, and a sintering process for heating and sintering an unsintered expanded PTFE porous film. ing.

  Usually, the expanded PTFE porous membrane obtained by such a production method is strongly oriented in the longitudinal direction (MD: longitudinal direction) in an extrusion process or a stretching process. In particular, in the stretching process, a fine structure composed of a large number of fine fibrils and a large number of nodes connected to each other by the fibrils is formed. At that time, the fibrils are strongly oriented in the stretching direction. Therefore, the expanded PTFE porous membrane exhibits anisotropy depending on the direction in the tensile strength. The tensile strength of the biaxially stretched PTFE porous membrane is greater in the machine direction (MD) than in the transverse direction (MD).

  The expanded porous PTFE membrane is easily torn when being sewn to a living tissue with a suture needle or suture. Fibrils themselves are very strong, and have a high tear strength in the direction of cutting the fibrils (lateral direction: TD) at the time of suturing using a suture thread, but a weak tear strength in the MD direction.

  Therefore, the expanded PTFE porous membrane generally has a large mechanical anisotropy. This tendency is remarkable in a uniaxially stretched PTFE porous membrane obtained by uniaxially stretching a rolled sheet in the longitudinal direction. In particular, a tubular expanded PTFE porous body has extremely strong mechanical anisotropy as described above because fibrils are strongly oriented in the longitudinal direction (MD) of the tube. Therefore, the sheet produced by cutting open the expanded PTFE porous tube also has strong mechanical anisotropy.

  Such mechanical anisotropy in tensile strength, tear strength, etc. also appears strongly in the biaxially stretched PTFE porous membrane. Moreover, such mechanical anisotropy is not eliminated even when the stretching ratio in the transverse direction (TD) is made larger than the stretching ratio in the machine direction (MD) during biaxial stretching.

  Such mechanical anisotropy is often a problem in many applications of expanded PTFE porous membranes. For example, in clothing applications, it is required that the expanded PTFE porous membrane does not tear or break with needles or threads during sewing. If the stretched PTE porous membrane has mechanical anisotropy and is easily broken by the yarn, such a requirement cannot be sufficiently met. In the field of in-vivo implant materials, it is required that the tear strength of a thread be strong in any direction when sewing with a suture. Further, the patch material is required to have uniform physical properties on the film surface.

  Conventionally, a medical prosthetic material has been proposed in which two or more expanded PTFE porous membranes are laminated with their main stretching directions intersecting each other at an arbitrary angle and integrated together (Patent Document 1). . According to this method, a laminated sheet with improved tear strength by the suture can be obtained. However, since the method described in Patent Document 1 needs to be laminated by crossing the stretching directions of two or more expanded PTFE porous membranes at an arbitrary angle, the process is complicated and the cost is high. In addition, in this method, since two or more expanded PTFE porous membranes cannot be laminated in the longitudinal direction, long products and large-area products cannot be manufactured. In addition, when this laminated sheet is trimmed to a desired shape with scissors, interfacial peeling is likely to occur at the cut surface and in the vicinity thereof, and sufficient strength against stitching may not be maintained.

  By heating to 300 ° C. or higher with the stretched porous PTFE film in close contact with the net-like solid structure, a nodule aggregate part and a non-nodule aggregate part having a longer internodal distance than the nodule aggregate part are formed. A method to do this has been proposed (Patent Document 2). According to this method, an expanded PTFE porous membrane having improved tear strength and tensile strength can be obtained without impairing the porous structure and flexibility. However, the expanded PTFE porous membrane obtained by the method described in Patent Document 2 has a non-aggregated portion with a non-aggregated portion because the coagulated portion and the non-aggregated portion of the nodule coexist. Furthermore, with this method, it is difficult to freely set the pore diameter of the expanded PTFE porous membrane.

  There has been proposed an in vivo transplant material in which a fluororesin layer having a pore size of 0.05 to 0.5 μm is formed on the outer surface of an expanded PTFE porous body (Patent Document 3). According to this method, an in vivo transplant material having improved tear strength against sutures, that is, suture tear strength, while suppressing the invasion and adhesion of surrounding tissues while maintaining flexibility and fluid fluidity. Can do. However, with this method, the pore diameter of the implant material cannot be set freely. In addition, this method cannot improve the mechanical anisotropy of the expanded PTFE porous membrane itself.

JP-A-54-90897 JP 7-82399 A JP-A-9-173438

  An object of the present invention is to provide a biaxially stretched polytetrafluoroethylene porous membrane in which the anisotropy due to the direction of the suture tear strength is substantially eliminated and the suture tear strength itself is improved without impairing flexibility. There is to do.

  Another object of the present invention is to provide a biaxially stretched polytetrafluoroethylene porous membrane in which anisotropy due to the direction of the tensile strength is substantially eliminated and the tensile strength itself is improved without impairing flexibility. There is to do.

  Another object of the present invention is that the anisotropy due to the direction of Suture tear strength and tensile strength is substantially eliminated without sacrificing flexibility, these strengths themselves are improved, and the porosity and pore diameter can be freely set. An object of the present invention is to provide a method for producing a biaxially stretched polytetrafluoroethylene porous membrane that can be designed.

  As a result of diligent research to solve the above problems, the inventors of the present invention have produced a biaxially stretched PTFE porous membrane in an unsintered state after the stretching step in the biaxially stretched PTFE porous membrane manufacturing process. By arranging the compression step, the anisotropy due to the direction of strength characteristics such as Suture tear strength and tensile strength is substantially eliminated without impairing the inherent flexibility of the expanded porous PTFE membrane, and the strength itself It has also been found that an improved biaxially stretched PTFE porous membrane can be obtained.

  According to the production method of the present invention, the porosity can be designed freely. Further, according to the production method of the present invention, a plurality of biaxially stretched PTFE porous membranes are overlapped and then compressed in the film thickness direction, and then heat-sintered to heat-bond each layer to be integrated. Thus, a homogeneous biaxially stretched PTFE porous membrane having a freely designed thickness can be obtained. The present invention has been completed based on these findings.

  According to the present invention, a biaxially stretched polytetrafluoroethylene porous membrane having a microstructure composed of fine fibrils and nodes connected by the fibrils, wherein the suture tear strength is in the machine direction (MD) and the transverse direction. (TD) is 300 gf or more, and the Suture tear strength difference in the machine direction (MD) and the transverse direction (TD) is 20% or less. Is provided.

  According to the present invention, there is also provided a biaxially stretched polytetrafluoroethylene porous membrane having a microstructure comprising fine fibrils and nodes connected by the fibrils, wherein the tensile strength is in the machine direction (MD) and the transverse direction. Biaxially stretched poly, characterized in that it is 2.5 kgf or more per 1 cm width in any direction (TD), and the difference in tensile strength between the machine direction (MD) and the transverse direction (TD) is 20% or less. A tetrafluoroethylene porous membrane is provided.

Furthermore, according to the present invention, there is provided a method for producing a biaxially stretched polytetrafluoroethylene porous membrane having a microstructure comprising fine fibrils and nodes connected by the fibrils, comprising the following steps 1 to 5:
(1) An extrusion process 1 in which a mixture of unsintered polytetrafluoroethylene powder and a lubricant is extruded to produce a sheet-shaped or rod-shaped extruded product;
(2) Rolling step 2 in which the extruded product is rolled to produce a rolled sheet;
(3) Stretching step 3 in which a rolled sheet is biaxially stretched in the longitudinal and lateral directions to produce a biaxially stretched sheet;
(4) Compression step 4 for producing a compressed sheet by compressing a biaxially stretched sheet in the film thickness direction;
(5) Sintering step 5 in which the compressed sheet is heated and sintered at a temperature equal to or higher than the melting point of polytetrafluoroethylene in a state where it is fixed so as not to shrink;
By this, a method for producing a biaxially stretched polytetrafluoroethylene porous membrane characterized by obtaining a biaxially stretched polytetrafluoroethylene porous membrane is provided.

Furthermore, according to the present invention, there is provided a method for producing a biaxially stretched polytetrafluoroethylene porous membrane having a microstructure composed of fine fibrils and nodes connected by the fibrils, comprising the following steps I to VI:
(1) Extrusion step I of extruding a mixture of unsintered polytetrafluoroethylene powder and a lubricant to produce a sheet-like or rod-like extrudate;
(2) Rolling step II of rolling an extruded product to produce a rolled sheet;
(3) A stretching step III in which a rolled sheet is biaxially stretched in the longitudinal direction and the transverse direction to produce a biaxially stretched sheet;
(4) Step IV of producing a multilayer sheet by superimposing two or more biaxially stretched sheets;
(5) Compression step V for compressing the multilayer sheet in the film thickness direction to produce a compressed multilayer sheet;
(6) The compressed multilayer sheet is heated and sintered at a temperature equal to or higher than the melting point of polytetrafluoroethylene in a state in which all the layers are fixed so as not to shrink, and at the same time, the respective layers are thermally fused and integrated. Sintering process VI;
By this, a method for producing a biaxially stretched polytetrafluoroethylene porous membrane characterized by obtaining a biaxially stretched polytetrafluoroethylene porous membrane is provided.

  According to the present invention, the anisotropy due to the direction of Suture tear strength and tensile strength is substantially eliminated without impairing the inherent flexibility of the biaxially stretched PTFE porous membrane, and the mechanical strength itself is also improved. In addition, a biaxially stretched PTFE porous membrane that can freely design the porosity and the pore diameter is provided.

  The biaxially-stretched PTFE porous membrane of the present invention is a single-layer membrane or a substantially single-layer membrane in which multiple layers are integrated, and has a uniform and high strength, so that dimension adjustment and trimming can be performed freely. . According to the present invention, a biaxially stretched PTFE porous membrane having no mechanical anisotropy, high strength, and a long or large area can be produced in a large amount at a low cost.

  The biaxially stretched PTFE porous membrane in which the mechanical anisotropy of the present invention is substantially eliminated can be produced by the following method. That is, the 1st manufacturing method of this invention has the following processes 1-5.

(1) An extrusion process 1 in which a mixture of unsintered polytetrafluoroethylene powder and a lubricant is extruded to produce a sheet-shaped or rod-shaped extruded product;
(2) Rolling step 2 in which the extruded product is rolled to produce a rolled sheet;
(3) Stretching step 3 in which a rolled sheet is biaxially stretched in the longitudinal and lateral directions to produce a biaxially stretched sheet;
(4) Compression step 4 for producing a compressed sheet by compressing a biaxially stretched sheet in the film thickness direction;
(5) Sintering step 5 in which the compressed sheet is heated and sintered at a temperature equal to or higher than the melting point of polytetrafluoroethylene in a state where the compressed sheet is fixed so as not to shrink.

  Extrusion step 1 can be performed according to methods well known in the art. As a specific example, it was obtained after a mixture of unsintered PTFE powder (fine powder for paste extrusion) and a lubricant (for example, solvent naphtha, petroleum, etc.) was compressed in a cylinder and preformed into a cylindrical shape. A preform (billet) is put into an extrusion cylinder, pressed with a ram, and extruded from a die to produce a sheet-shaped or rod-shaped extruded product. In order to obtain a sheet-like extrudate, a T-shaped die is connected to the tip of the extrusion cylinder, and in order to obtain a rod-like extrudate, a circular opening die is used.

  The rolling process 2 can also be performed according to a conventional method. The sheet-like or rod-like extrudate obtained in the extrusion step is rolled using a rolling device such as a roll or a press before the lubricant is volatilized to produce a rolled sheet having a predetermined thickness. A larger rolling ratio is preferable. For example, when the extrudate is a sheet, the rolling ratio T1 / T2 represented by the value obtained by dividing the film thickness T1 before rolling by the film thickness T2 after rolling is preferably more than 1.3 times, more preferably Is 1.6 times or more, particularly preferably 2.0 times or more.

  If the rolling ratio is too small, stretching unevenness is likely to occur in the biaxially stretched PTFE porous membrane in the stretching step. By increasing the rolling ratio, it is possible to suppress stretching unevenness and improve mechanical anisotropy and mechanical strength in combination with other processes. The upper limit of the rolling ratio is usually about 10 times, preferably about 8 times, more preferably about 5 times. When the extruded product is rod-shaped, the rolling ratio is adjusted in consideration of the thickness when the rod is formed into a sheet.

  The film thickness of the rolled sheet can be appropriately set as necessary, but is usually in the range of 0.3 to 2.0 mm, preferably 0.4 to 1.5 mm, particularly preferably 0.5 to 1.3 mm. It is. If the thickness of the rolled sheet is too thin, it becomes difficult to increase the stretching ratio, or the thickness of the biaxially stretched PTFE porous film (unsintered biaxially stretched sheet) becomes too thin. If the rolled sheet is too thick, uniform stretching may be difficult.

  The rolled sheet is biaxially stretched with or without removing the lubricant from the rolled sheet. When the lubricant is not removed from the rolled sheet, the lubricant is removed in a subsequent process such as a stretching process. In the case of removing the lubricant from the rolled sheet, for example, a method of volatilizing the lubricant through the drying sheet at 100 to 300 ° C. can be employed.

  In the stretching step 3, the rolled sheet is biaxially stretched in the longitudinal direction and the transverse direction to produce a biaxially stretched PTFE porous membrane (hereinafter referred to as “biaxially stretched sheet”) in an unsintered state. As the biaxial stretching method of the rolled sheet, a simultaneous biaxial stretching method or a sequential biaxial stretching method can be adopted, but first, stretching is performed in the machine direction (MD; longitudinal direction or longitudinal direction), and then transverse direction. It is preferable to employ a sequential biaxial stretching method in which stretching is performed in the direction (TD; width direction). In the sequential biaxial stretching method, for example, it is preferable to employ a method of stretching in the machine direction (MD) between a low-speed roll and a high-speed roll and then stretching in the transverse direction (TD) using a tenter.

  The machine direction (MD) stretch ratio in biaxial stretching is usually 1.2 to 10.0 times, preferably 1.5 to 8.0 times, and more preferably 2.0 to 5.0 times. Moreover, a transverse direction (TD) draw ratio is 3.0-20.0 times normally, Preferably it is 4.0-15.0 times, More preferably, it is 5.0-13.0 times. In the production method of the present invention, biaxial stretching is performed so that the TD stretch ratio is larger than the MD stretch ratio, and the biaxial stretching with small mechanical anisotropy is performed through the subsequent compression process and sintering process. Since a PTFE porous membrane is easily obtained, it is preferable.

  In the stretching step 3, biaxially so that the total stretching ratio E1 × E2 represented by the product of the MD stretching ratio E1 and the TD stretching ratio E2 is usually 12 times or more, preferably 15 times or more, more preferably 20 times or more. It is desirable to perform stretching. If the total draw ratio is too small, even if the biaxially stretched sheet is compressed, the mechanical anisotropy cannot be sufficiently improved without impairing flexibility. The upper limit of the total draw ratio is usually about 40 times, preferably about 30 times. The total draw ratio can be controlled to a desired range by adjusting the MD draw ratio and the TD draw ratio within the above ranges.

  The unsintered biaxially stretched sheet obtained in the stretching step 3 preferably has a porosity of 70% or more. The upper limit of the porosity of the biaxially stretched sheet is usually 90%, preferably about 87%. By setting the total stretch ratio high and increasing the porosity of the obtained biaxially stretched sheet, the porosity of the biaxially stretched PTFE porous membrane obtained in the subsequent compression step and sintering step can be increased. By increasing the porosity of the biaxially stretched PTFE porous membrane as the final product, the flexibility can be maintained at a high level and the characteristics as a porous body can be sufficiently exhibited.

  In the compression step 4, the unsintered biaxially stretched sheet is compressed in the film thickness direction to reduce the film thickness. In the compression step, the biaxially stretched sheet is compressed using a rolling roll or a press. In the manufacturing process of the biaxially stretched PTFE porous membrane of the present invention, since the rolling process is already performed once in the rolling process 2 before the compressing process 4, the compression in the compressing process is called “re-rolling”, and the compressing process. May be referred to as a “re-rolling step”.

  In the compression step 4, the compression ratio t1 / t2 represented by the value obtained by dividing the film thickness t1 before compression by the film thickness t2 after compression is usually 1.2 or more, preferably 1.5 or more, more preferably 1.8. As described above, the biaxially stretched sheet is compressed so as to be particularly preferably 2.0 or more. The upper limit of the compression ratio is usually 4.0, preferably about 3.0.

  If the compression ratio in the compression step 4 is too small, the effect of suppressing the mechanical anisotropy becomes insufficient and the effect of improving the mechanical strength is also lowered. When the compression ratio is too large, the film thickness becomes too thin or the porosity becomes too small.

  In the sintering step 5, the compressed compressed sheet in an unsintered state is heated and sintered to a temperature equal to or higher than the melting point (327 ° C.) of PTFE while being fixed so as not to shrink. This sintering process can be normally carried out through a compressed sheet in a furnace having an atmosphere of 330 to 500 ° C, preferably 340 to 400 ° C. By sintering, a biaxially stretched PTFE porous membrane in which the biaxially stretched and compressed state is sintered and fixed, the mechanical anisotropy is suppressed, and the strength is improved can be obtained.

  In the sintering step 5, a biaxially stretched PTFE porous membrane having a porosity of preferably 40% or more, more preferably 45% or more, and particularly preferably 50% or more is produced. The upper limit of the porosity of the sintered biaxially stretched PTFE porous membrane is usually about 80%, preferably about 75%. By setting the total draw ratio high to increase the porosity of the biaxially stretched sheet, a biaxially stretched PTFE porous membrane having a relatively high porosity and excellent flexibility in the subsequent compression step can be obtained. It becomes easy.

  The film thickness of the biaxially stretched PTFE porous membrane obtained by sintering is usually 0.02 to 1.0 mm, preferably 0.03 to 0.8 mm, more preferably 0.04 to 0.5 mm, particularly preferably. Is 0.05 to 0.3 mm.

  The pore diameter of the biaxially stretched PTFE porous membrane of the present invention can be freely set by controlling the stretching conditions in the stretching step. When a biaxially stretched PTFE porous membrane is used as a transplant material, it is necessary to select the pore size depending on the site and purpose of use.

  In order to apply the biaxially stretched PTFE porous membrane to an application that requires maintaining flexibility while suppressing tissue penetration, it is preferable that the porosity is 40% or more and the thickness is 1 mm or less. Moreover, it is preferable that the bubbling point using isopropyl alcohol is 100 kPa or more, the pore diameter is 0.45 μm or less, and the fiber length is 10 μm or less.

  When the biaxially stretched PTFE porous membrane is applied to an application requiring tissue healing properties, the bubbling point is preferably 50 kPa or less, the pore diameter is 1 μm or more, and the fiber length is 20 μm or more, the bubbling point is 1 kPa or less, It is more preferable that the pore diameter is 5 μm or more and the fiber length is 60 μm or more in order to improve the curability.

  The biaxially stretched PTFE porous membrane of the present invention is a porous body having a fine structure composed of fine fibrils and nodes connected by the fibrils. The biaxially stretched PTFE porous membrane of the present invention has a suture tear strength of 300 gf or more in both the machine direction (MD) and the transverse direction (TD), and the suture in the machine direction (MD) and the transverse direction (TD). The difference in tear strength is 20% or less.

  Suture tear strength is a value measured by the measurement method described in the examples described later. A suture is a suture thread. The suture thread is passed through a biaxially stretched PTFE porous membrane, and both ends of the threaded suture thread are loaded into the load cell using a measuring device (Autograph AG500E manufactured by Shimadzu Corporation). The suture is pulled at a speed of 20 mm / min, fixed to the grip on the side, and the maximum load generated when the suture is completely pulled off from the sheet is defined as the suture tension strength. The degree of anisotropy can be evaluated by measuring the suture tear strength in the MD direction and the TD direction of the biaxially stretched PTFE porous membrane.

  Suture tear strength indicates a practical strength characteristic when a biaxially stretched PTFE porous membrane is sutured using a needle and a thread. The Suture tear strength of the biaxially stretched PTFE porous membrane of the present invention is preferably 400 gf or more, more preferably 450 gf or more, in both MD and TD. Further, the Suture tear strength difference between MD and TD is preferably 15% or less, more preferably 10% or less.

  According to the conventional manufacturing method, even if the stretching ratio in the transverse direction (TD) is larger than the stretching ratio in the longitudinal direction (MD), the biaxially stretched PTFE porous membrane having extremely low Suture tear strength in the longitudinal direction (MD) I could only get it. On the other hand, according to the manufacturing method of the present invention in which the compression step is arranged after the stretching step, the anisotropy of the suture tear strength due to such a direction can be substantially eliminated, and the value of the suture tear strength is obtained. Can raise itself.

  In the biaxially stretched PTFE porous membrane of the present invention, anisotropy in tensile strength is substantially eliminated. That is, the biaxially stretched PTFE porous membrane of the present invention has a tensile strength of 2.5 kgf or more per 1 cm width both in the machine direction (MD) and the transverse direction (TD), and in the machine direction (MD) and the transverse direction. The difference in tensile strength in the direction (TD) is 20% or less.

  The tensile strength of the biaxially stretched PTFE porous membrane of the present invention is preferably 2.8 kgf / cm or more, more preferably 3.0 kgf / cm or more, in both MD and TD. Further, the difference in tensile strength between MD and TD is preferably 15% or less, more preferably 10% or less.

  According to the conventional manufacturing method, even if the stretching ratio in the transverse direction (TD) is larger than the stretching ratio in the longitudinal direction (MD), only a biaxially stretched PTFE porous membrane having a low tensile strength in the transverse direction (TD) is obtained. I couldn't. On the other hand, according to the manufacturing method of the present invention in which the compression step is arranged after the stretching step, the anisotropy of the tensile strength due to such a direction can be substantially eliminated, and the value of the tensile strength itself can be obtained. Can be high.

  In the first production method of the present invention, since it is preferable to increase the rolling ratio, the draw ratio, and the compression ratio, the film thickness of the obtained single-layer biaxially stretched PTFE porous film is often thin. For applications where a biaxially stretched PTFE porous membrane having a large film thickness is required, a multilayering step can be arranged to increase the film thickness. That is, the second production method of the present invention includes the following steps I to VI.

(1) Extrusion step I of extruding a mixture of unsintered polytetrafluoroethylene powder and a lubricant to produce a sheet-like or rod-like extrudate;
(2) Rolling step II of rolling an extruded product to produce a rolled sheet;
(3) A stretching step III in which a rolled sheet is biaxially stretched in the longitudinal direction and the transverse direction to produce a biaxially stretched sheet;
(4) Step IV of producing a multilayer sheet by superposing two or more biaxially stretched sheets;
(5) Compression step V in which the multilayer sheet is compressed in the film thickness direction to produce a compressed multilayer sheet;
(6) The compressed multilayer sheet is heated and sintered at a temperature equal to or higher than the melting point of polytetrafluoroethylene in a state where all the layers are fixed so as not to shrink, and at the same time, the respective layers are thermally fused and integrated. Sintering process VI.

  The extrusion process I, the rolling process II, and the stretching process III in the second manufacturing method correspond to the extrusion process 1, the rolling process 2, and the stretching process 3 in the first manufacturing method, respectively. In the second production method of the present invention, a point where the multilayering step IV is arranged, a step V where the multilayer sheet is compressed, and a sintering step VI where the respective layers are thermally fused and integrated simultaneously with the sintering are arranged. It is characterized by a point.

  In the multilayering step, two or more unsintered biaxially stretched sheets obtained in the stretching step are overlapped to produce a multilayer sheet. This multilayer sheet is not integrated in a state where the respective layers are separated. The number of unsintered biaxially stretched sheets used for the production of the multilayer sheet can be appropriately determined in consideration of the film thickness and the film thickness of the biaxially stretched PTFE porous film that is finally required. . The number of sheets is usually 2 to 30, preferably 2 to 20, and more preferably 3 to 15. However, the number is not limited to these.

  In the compression step V, the multilayer sheet is compressed in the film thickness direction to reduce the film thickness. In the compression step, the multilayer sheet is compressed so that the compression ratio is usually 1.2 or more, preferably 1.5 or more, more preferably 1.8 or more, and particularly preferably 2.0 or more. The upper limit of the compression ratio is usually 4.0, preferably about 3.0.

  In the sintering step VI, the compressed multilayer sheet is heated and sintered at a temperature equal to or higher than the melting point of PTFE in a state where all the layers are fixed so as not to shrink, and at the same time, the respective layers are thermally fused and integrated. A biaxially stretched PTFE porous membrane is prepared. The sintering conditions such as the sintering temperature are the same as those in the sintering process of the first manufacturing method, but in the second manufacturing method, each layer is heated by using heating for sintering in the sintering process. Is heat-sealed. When the respective layers are heat-sealed, one biaxially stretched PTFE porous membrane in which all the layers are integrated is obtained.

  In the sintering step VI, a biaxially stretched PTFE porous membrane having a porosity of preferably 40% or more, more preferably 45% or more, and particularly preferably 50% or more is produced. The upper limit of the porosity of the sintered biaxially stretched PTFE porous membrane is usually about 80%, preferably about 75%. By setting the total draw ratio high to increase the porosity of the biaxially stretched sheet, a biaxially stretched PTFE porous membrane having a relatively high porosity and excellent flexibility in the subsequent compression step can be obtained. It becomes easy.

  Although the film thickness of the biaxially stretched PTFE porous membrane obtained in the sintering step VI can be set according to the use, it is usually 0.04 to 2.0 mm, preferably 0.06 to 1.6 mm. Preferably it is 0.08-1.3 mm, Most preferably, it is 0.1-1.1 mm. When the biaxially stretched PTFE porous membrane obtained after the compression step is used as a cushioning material or a sealing material, a product thickness of about 2.0 mm or more, or about 3.0 to 10.0 mm may be required. In such a case, it is desirable to adjust the thickness of the multilayer sheet so that it exceeds 2.0 mm, and more preferably 5.0 to 30.0 mm.

  The biaxially stretched PTFE porous membrane obtained by the second production method is also substantially free from mechanical anisotropy and is the same as the biaxially stretched PTFE porous membrane obtained by the first production method. Each characteristic of Suture tear strength and tensile strength is shown. In addition, since the layers are compressed and further sintered after the multilayering, the respective layers are fused and integrated, and delamination does not occur.

  According to the second production method of the present invention, since a plurality of long biaxially stretched sheets can be superposed in the machine direction (MD; length direction), the multilayering operation is simple and continuous. Long products and large-area products can be easily manufactured.

  The biaxially stretched PTFE porous membrane obtained by the first and second production methods of the present invention may be used as it is for various applications, or, if necessary, laminated with other layers or substrates, Hydrophilic treatment can be performed.

  The biaxially stretched PTFE porous membrane of the present invention can be used by cutting into an appropriate shape and size as a sealing material, cushioning material, or spacer. The biaxially stretched PTFE porous membrane of the present invention can be used for production of various clothing items such as trekking wear, rain wear, ski wear, shoes, and gloves. The biaxially stretched PTFE porous membrane of the present invention has substantially no mechanical anisotropy, and is a single-layer membrane or a membrane in which layers are substantially fused and integrated, and has high strength and homogeneity. Can be trimmed into a desired shape using a cutting tool such as scissors, etc., thereby preventing delamination, decreasing strength, and causing anisotropy depending on direction. . Moreover, since the biaxially-stretched PTFE porous membrane of the present invention is excellent in stitchability, it can be easily processed into various clothing items.

  The biaxially stretched PTFE porous membrane of the present invention can be used as an in vivo implant material as it is in the form of a membrane, or after being molded into an appropriately shaped structure or by performing various secondary processes. it can. The biaxially stretched PTFE porous membrane of the present invention has substantially uniform physical properties in all directions on the membrane surface, and is excellent in Suture tear strength and tensile strength. Therefore, the pericardium, pleura, diaphragm, peritoneum, It is suitable as a patch material used for repairing a tendon sheath or the like. In addition, the biaxially stretched PTFE porous membrane of the present invention can be used as a medical polymer material such as an artificial blood vessel, a catheter, and an artificial cartilage substitute material by secondary processing. The biaxially stretched PTFE porous membrane of the present invention can be easily sewn to a living tissue with a suture.

  The biaxially stretched PTFE porous film of the present invention can be used as a base film of an anisotropic conductive film. The anisotropic conductive film can be produced, for example, by a method in which a plurality of through holes are formed in a biaxially stretched PTFE porous film and a conductive metal is selectively attached only to the wall surface of each through hole. In order to selectively attach conductive metal only to the wall surface of each through hole, a plating mask material is placed on both sides, a plating catalyst is applied only to each through hole, the mask is removed, and electroless plating is performed. Furthermore, a method of performing electroplating as needed is mentioned. Such an anisotropic conductive film can be used for electrical bonding between circuit elements in a semiconductor device or the like, or for inspection of electrical reliability in a circuit board or the like.

  Furthermore, since the biaxially stretched PTFE porous membrane of the present invention is excellent in strength properties, it can be used alone, for example, stretched with a large pore diameter and high porosity with high healing properties when used as an in vivo implant material, for example. It can also be used as a reinforcing material for porous PTFE, a reinforcing material for woven or non-woven fabric made of polyester resin such as polyethylene terephthalate, and the like.

  Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples. The measuring method of various characteristics in the present invention is as follows.

(1) Rolling ratio and re-rolling ratio:
A value T1 / T2 obtained by dividing the thickness T1 of the extruded sheet before rolling by the thickness T2 after rolling was defined as a rolling ratio. A value t1 / t2 obtained by dividing the film thickness t1 before rerolling of the biaxially stretched porous PTFE film by the film thickness t2 after rerolling was defined as a rerolling ratio (compression ratio).

(2) Stretch ratio:
2-1. Machine direction (MD) draw ratio:
The longitudinal draw ratio was calculated by the following formula (i).
Longitudinal direction (MD) draw ratio = finished speed of finished product (winding speed) / feed rate of material before drawing (i)

2-2. Transverse direction (TD) draw ratio:
The transverse draw ratio was calculated by the following formula (ii).
Transverse direction (TD) Stretch ratio = Distance between tenter chucks before stretching / Distance between tenter chucks after stretching (ii)

2-3. Total draw ratio:
The total draw ratio was calculated by the following formula (iii).
Total draw ratio = MD draw ratio × TD draw ratio (iii)

(3) Porosity:
The volume was determined based on the difference between the dry weight of the biaxially stretched PTFE porous membrane and the weight in water. The true specific gravity of PTFE was 2.25 g / cc, and the volume of the resin was calculated from the true specific gravity and the dry weight of the biaxially stretched PTFE porous membrane. The void volume was calculated by subtracting the volume of the resin from the volume of the biaxially stretched PTFE porous membrane.
The porosity (%) was calculated by the following formula (iv).
(Void volume / volume) × 100 (iv)

(4) Film thickness:
Using a dial gauge (Model No. 547-301 manufactured by Mitutoyo), the film thickness of the sample was measured at four points, and the average value was taken as the film thickness of the sample.

(5) Suture tear strength:
A biaxially-stretched PTFE porous membrane was cut into a rectangular shape having a length of 2 cm and a width of 1 cm along the longitudinal direction (MD: longitudinal direction) and the lateral direction (TD: width direction), respectively, and a sheet-like sample Was made. The suture was passed through the sheet by puncturing a needle with a plastic needle (Ethicon Proline 6-0, product number M8307) 2 mm from one edge of the sheet and centered from both edges. .

  Shimadzu Autograph AG500E was used as a measuring device. Fix the other end of the sheet to the grip on the crosshead side, fix both ends of the suture thread that passed through the sheet to the grip on the load cell side, and pull the suture at a speed of 20 mm / min. The maximum load generated when pulled until separation was defined as the suture tear strength (unit: gf).

Suture-tear strength is measured in each of 6 points in the machine direction (MD) and transverse direction (TD) of the sheet, and the average value of each is taken in the machine direction (MD) Suture tear strength and transverse direction (TD) Suture tear. Strength. The tear strength difference (%) was calculated by the following formula (v).
√ {(MD tear strength−TD tear strength) ² } ÷ (MD tear strength + TD tear strength) × 100% (v)

(6) Tensile strength:
A biaxially stretched PTFE porous membrane was cut out into a rectangle having a length of 6 cm and a width of 1 cm along the longitudinal direction (MD: longitudinal direction) and the transverse direction (TD: width direction), respectively, and a sheet-like sample Was made. Shimadzu Autograph AG500E was used as a measuring device. The grip interval was set to 20 mm, the sheet was fixed to the crosshead side grip and the load cell side grip one by one, and tensile strain was applied until the sheet broke at a speed of 20 mm / min.

Tensile strength was measured in each of four points in the machine direction (MD) and transverse direction (TD) of the sheet, and the respective average values were taken as machine direction (MD) tensile strength and transverse direction (TD) tensile strength ( Unit = kgf / cm). The tensile strength difference (%) was calculated by the following formula (vi).
√ {(MD tensile strength−TD tensile strength) ² } ÷ (MD tensile strength + TD tensile strength) × 100% (vi)

[Example 1]
20 parts by weight of naphtha was blended and mixed with 100 parts by weight of PTFE fine powder (F104) manufactured by Daikin Industries. The mixture was allowed to stand at 60 ° C. for about 24 hours to familiarize each component. Next, this mixture was compressed in a cylinder having an inner diameter of about 130 mm and preformed. The cylindrical preform was put into an extrusion cylinder having an inner diameter of 130 mm, and extruded from a T-shaped die into a sheet having a width of 150 mm and a thickness of 2 mm. Next, the sheet-like extrudate was rolled at a rolling ratio of 2.0 and a film thickness of 1.00 mm.

  The rolled sheet obtained above was successively biaxially stretched at respective stretching ratios of 2.25 times at 200 ° C. in the machine direction (MD) and then 11.00 times at 200 ° C. in the transverse direction (TD). The total draw ratio was 24.75. The stretched sheet obtained had a porosity of 83% and a film thickness of 0.27 mm. This stretched sheet was re-rolled with a roll mill so that the film thickness was 0.11 mm (re-rolling ratio 2.5). Next, the obtained re-rolled sheet was passed through a furnace having an atmosphere of 350 ° C. for sintering. The biaxially stretched PTFE porous membrane thus obtained was very flexible, had a porosity of 56% and a thickness of 0.10 mm. The results are shown in Table 1.

[Example 2]
20 parts by weight of naphtha was blended and mixed with 100 parts by weight of PTFE fine powder (F104) manufactured by Daikin Industries. The mixture was allowed to stand at 60 ° C. for about 24 hours to familiarize each component. Next, this mixture was compressed in a cylinder having an inner diameter of about 130 mm and preformed. The cylindrical preform was put into an extrusion cylinder having an inner diameter of 130 mm, and extruded from a T-shaped die into a sheet having a width of 150 mm and a thickness of 2 mm. Next, the sheet-like extrudate was rolled at a rolling ratio of 1.6 and a film thickness of 1.25 mm.

  The rolled sheet obtained above was successively biaxially stretched at respective stretching ratios of 2.25 times at 200 ° C. in the longitudinal direction and then 11.00 times at 200 ° C. in the transverse direction. The total draw ratio was 24.75. The obtained stretched sheet had a porosity of 84% and a film thickness of 0.35 mm. This stretched sheet was re-rolled with a roll mill so that the film thickness was 0.16 mm (re-rolling ratio 2.2). Next, the obtained re-rolled sheet was passed through a furnace having an atmosphere of 350 ° C. for sintering. The biaxially stretched PTFE porous membrane thus obtained was very flexible, had a porosity of 58% and a thickness of 0.14 mm. The results are shown in Table 1.

[Comparative Example 1]
20 parts by weight of naphtha was blended and mixed with 100 parts by weight of PTFE fine powder (F104) manufactured by Daikin Industries. The mixture was allowed to stand at 60 ° C. for about 24 hours to familiarize each component. Next, this mixture was compressed in a cylinder having an inner diameter of about 130 mm and preformed. The cylindrical preform was put into an extrusion cylinder having an inner diameter of 130 mm, and extruded from a T-shaped die into a sheet having a width of 150 mm and a thickness of 2 mm. Next, the sheet-like extrudate was rolled at a rolling ratio of 2.0 and a film thickness of 1.00 mm.

  The rolled sheet obtained above was successively biaxially stretched at respective stretching ratios of 2.25 times at 200 ° C. in the longitudinal direction and then 11.00 times at 200 ° C. in the transverse direction. The total draw ratio was 24.75. The stretched sheet obtained had a porosity of 83% and a film thickness of 0.27 mm. Next, the drawn sheet was passed through a furnace at 350 ° C. for sintering. The biaxially stretched PTFE porous membrane thus obtained was very flexible, had a porosity of 72% and a thickness of 0.18 mm. The results are shown in Table 1.

[Comparative Example 2]
20 parts by weight of naphtha was blended and mixed with 100 parts by weight of PTFE fine powder (F104) manufactured by Daikin Industries. The mixture was allowed to stand at 60 ° C. for about 24 hours to familiarize each component. Next, this mixture was compressed in a cylinder having an inner diameter of about 130 mm and preformed. The cylindrical preform was put into an extrusion cylinder having an inner diameter of 130 mm, and extruded from a T-shaped die into a sheet having a width of 150 mm and a thickness of 2 mm. Next, the sheet-like extrudate was rolled at a rolling ratio of 1.6 and a film thickness of 1.25 mm.

  The rolled sheet obtained above was successively biaxially stretched at respective stretching ratios of 2.25 times at 200 ° C. in the longitudinal direction and then 11.00 times at 200 ° C. in the transverse direction. The total draw ratio was 24.75. The obtained stretched sheet had a porosity of 84% and a film thickness of 0.35 mm. Next, the drawn sheet was passed through a furnace at 350 ° C. for sintering. The biaxially stretched PTFE porous membrane thus obtained was very flexible, had a porosity of 72% and a thickness of 0.26 mm. The results are shown in Table 1.

[Comparative Example 3]
20 parts by weight of naphtha was blended and mixed with 100 parts by weight of PTFE fine powder (F104) manufactured by Daikin Industries. The mixture was allowed to stand at 60 ° C. for about 24 hours to familiarize each component. Next, this mixture was compressed in a cylinder having an inner diameter of about 130 mm and preformed. The cylindrical preform was put into an extrusion cylinder having an inner diameter of 130 mm, and extruded from a T-die into a sheet having a width of 150 mm and a thickness of 2 mm. Next, the sheet-like extrudate was rolled at a rolling ratio of 1.3 and a film thickness of 1.50 mm.

  The rolled sheet obtained above was successively biaxially stretched at respective stretching ratios of 2.25 times at 200 ° C. in the longitudinal direction and then 11.00 times at 200 ° C. in the transverse direction. The total draw ratio was 24.75. The stretched sheet obtained had a porosity of 86% and a film thickness of 0.48 mm. Next, the drawn sheet was passed through a furnace at 350 ° C. for sintering. The biaxially stretched porous PTFE membrane thus obtained was very flexible, had a porosity of 72% and a thickness of 0.28 mm. However, the biaxially stretched PTFE porous membrane was visually observed and found to have stretch unevenness. The results are shown in Table 1.

<Discussion>
The expanded porous PTFE membrane is usually strongly oriented in the longitudinal direction (MD: longitudinal direction) in the extrusion process and the stretching process. Therefore, the expanded PTFE porous membrane generally has a large mechanical anisotropy. This tendency is particularly remarkable in a uniaxially stretched PTFE porous membrane obtained by uniaxially stretching an extruded sheet or a rolled sheet in the longitudinal direction after the extrusion step.

  Even in a biaxially stretched PTFE porous membrane, it is difficult to reduce the mechanical anisotropy. That is, as shown in Comparative Examples 1 to 3, the transverse direction (TD: width direction) stretch ratio is considerably larger than the longitudinal direction (MD) stretch ratio to strengthen the transverse direction (TD) orientation. However, the mechanical anisotropy of the biaxially stretched PTFE porous membrane cannot be eliminated, and it is easy to tear in the machine direction (MD). Therefore, the Suture tear strength of these biaxially stretched PTFE porous membranes is strong in the transverse direction (TD) but weak in the longitudinal direction (MD).

  The tensile strength of these biaxially stretched PTFE porous membranes is high in the machine direction (MD) and low in the transverse direction (TD) (Comparative Example 1). Thus, it can be seen that the tensile strength is also large. In addition, although the tensile strength was not measured about the biaxially-stretched PTFE porous membrane of Comparative Examples 2 and 3, since the anisotropy of Suture tear strength is large as in Comparative Example 1, It is estimated that the anisotropy is large. Since uneven stretching occurred in Comparative Example 3, it can be seen that it is better to make the rolling ratio of the extruded sheet larger than 1.3.

  On the other hand, in Example 1, although it operated on the conditions similar to Comparative Example 1 until the biaxial stretching process, the re-rolling process is arrange | positioned after an extending process, and the biaxially stretched PTFE porous membrane before sintering Since the biaxially stretched PTFE porous film obtained after sintering is compressed in the film thickness direction, the mechanical anisotropy in the machine direction (MD) and the transverse direction (TD) is substantially eliminated. . Specifically, in the biaxially stretched PTFE porous membrane of Example 1, the difference in strength depending on the direction of Suture tear strength and tensile strength is remarkably small, and these strengths themselves are greatly improved.

  Since the biaxially stretched PTFE porous membrane of Example 2 is also provided with a compression step after the stretching step, the strength difference due to the direction of Suture tear strength is remarkably small, and the tear strength itself is greatly improved. Yes. In Example 2, the tensile strength was not measured, but the anisotropy due to the direction of the Suture tear strength was small and the same operation as in Example 1 was performed. It is clear that

  According to the production method of the present invention, a biaxially stretched PTFE porous membrane having a sufficient strength can be obtained with a single layer membrane, so that it is possible to produce a large, long and large area product at low cost. In addition, the biaxially stretched PTFE porous membrane of the present invention is substantially free from mechanical anisotropy and has a uniform strength with a single layer membrane. It can be used by trimming into a shape, whereby strength does not decrease and anisotropy due to direction does not occur.

  The biaxially stretched PTFE porous membrane of the present invention includes, for example, (1) sealing materials, cushion materials, spacers, (2) various clothing items such as trekking wear, rain wear, ski wear, shoes, gloves, and (3) patches. It can be used as medical materials such as materials, artificial blood vessels, catheters, artificial cartilage substitute materials, and (4) base films of anisotropic conductive films.

  In particular, the biaxially-stretched PTFE porous membrane of the present invention is used for sutures such as apparel materials and transplant materials used to replace living body tubular structures and septums lost due to diseases or injuries such as artificial blood vessels and patches. It can utilize suitably for the use in which operation is performed.

Claims (14)

  A biaxially stretched polytetrafluoroethylene porous membrane having a microstructure composed of fine fibrils and nodes connected by the fibrils, and having a suture tear strength in either the machine direction (MD) or the transverse direction (TD) The biaxially stretched polytetrafluoroethylene porous membrane is characterized in that the difference in the shear tear strength in the machine direction (MD) and the transverse direction (TD) is 20% or less.   A biaxially stretched polytetrafluoroethylene porous membrane having a microstructure composed of fine fibrils and nodes connected by the fibrils, and has a tensile strength in both the machine direction (MD) and the transverse direction (TD) A biaxially stretched polytetrafluoroethylene porous membrane characterized by being 2.5 kgf or more per 1 cm width and having a tensile strength difference of 20% or less in the machine direction (MD) and the transverse direction (TD). A method for producing a biaxially stretched polytetrafluoroethylene porous membrane having a microstructure comprising fine fibrils and nodes connected by the fibrils, comprising the following steps 1 to 5:
(1) An extrusion process 1 in which a mixture of unsintered polytetrafluoroethylene powder and a lubricant is extruded to produce a sheet-shaped or rod-shaped extruded product;
(2) Rolling step 2 in which the extruded product is rolled to produce a rolled sheet;
(3) Stretching step 3 in which a rolled sheet is biaxially stretched in the longitudinal and lateral directions to produce a biaxially stretched sheet;
(4) Compression step 4 for producing a compressed sheet by compressing a biaxially stretched sheet in the film thickness direction;
(5) Sintering step 5 in which the compressed sheet is heated and sintered at a temperature equal to or higher than the melting point of polytetrafluoroethylene in a state where it is fixed so as not to shrink;
A method for producing a biaxially stretched polytetrafluoroethylene porous membrane, characterized in that a biaxially stretched polytetrafluoroethylene porous membrane is obtained. A method for producing a biaxially stretched polytetrafluoroethylene porous membrane having a microstructure comprising fine fibrils and nodes connected by the fibrils, comprising the following steps I to VI:
(1) Extrusion step I of extruding a mixture of unsintered polytetrafluoroethylene powder and a lubricant to produce a sheet-like or rod-like extrudate;
(2) Rolling step II of rolling an extruded product to produce a rolled sheet;
(3) A stretching step III in which a rolled sheet is biaxially stretched in the longitudinal direction and the transverse direction to produce a biaxially stretched sheet;
(4) Step IV of producing a multilayer sheet by superposing two or more biaxially stretched sheets;
(5) Compression step V in which the multilayer sheet is compressed in the film thickness direction to produce a compressed multilayer sheet;
(6) The compressed multilayer sheet is heated and sintered at a temperature equal to or higher than the melting point of polytetrafluoroethylene in a state in which all the layers are fixed so as not to shrink, and at the same time, the respective layers are thermally fused and integrated. Sintering process VI;
A process for producing a biaxially stretched polytetrafluoroethylene porous membrane, characterized in that a biaxially stretched polytetrafluoroethylene porous membrane is obtained.   The production method according to claim 3 or 4, wherein in the rolling step 2 or II, the extruded product is rolled at a rolling ratio exceeding 1.3 times.   The production method according to claim 3 or 4, wherein in the stretching step 3 or III, biaxial stretching is performed so that the total stretching ratio is 12 times or more.   In the stretching step 3 or III, the machine direction (MD) stretch ratio is 1.2 to 10.0 times, the transverse direction (TD) stretch ratio is 3.0 to 20.0 times, and more than the MD stretch ratio. The production method according to claim 3 or 4, wherein biaxial stretching is performed so that a TD stretching ratio is larger.   The production method according to claim 3 or 4, wherein a biaxially stretched sheet having a porosity of 70% or more is produced in the stretching step 3 or III.   The manufacturing method of Claim 3 or 4 which compresses a biaxially stretched sheet or a multilayer sheet by the compression ratio 1.5 or more in the compression process 4 or V.   The production method according to claim 3 or 4, wherein a sintered biaxially stretched polytetrafluoroethylene porous membrane having a porosity of 40% or more is obtained in the sintering step 5 or VI.   In the sintering process 5 or VI, the suture tear strength is 300 gf or more in both the longitudinal direction (MD) and the transverse direction (TD), and the difference in the suture tear strength between the longitudinal direction (MD) and the transverse direction (TD) is The production method according to claim 3 or 4, wherein a sintered biaxially stretched polytetrafluoroethylene porous membrane of 20% or less is obtained.   In the sintering step 5 or VI, the tensile strength is 2.5 kgf or more per 1 cm width both in the machine direction (MD) and the transverse direction (TD), and in the machine direction (MD) and the transverse direction (TD). The production method according to claim 3 or 4, wherein a sintered biaxially stretched polytetrafluoroethylene porous film having a tensile strength difference of 20% or less is obtained.   An article of clothing produced using the biaxially stretched polytetrafluoroethylene porous membrane according to claim 1.   An in vivo implant material produced using the biaxially stretched polytetrafluoroethylene porous membrane according to claim 1 or 2.